This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Objective: To determine the facilitators of good parenting in primates. As in humans, cooperative breeding marmosets and tamarins show a considerable amount of father directed infant care. However, marmoset and tamarin fathers spend more time than the mother caring for infants. Fathers before delivery show hormonal changes that facilitate infant responsiveness. We found that experienced father marmosets are highly but variably responsive to infants. Males tested for their infant responsiveness are highly motivated to respond to a live infant or to vocalizations produced by an infant. We found that males with lowered prolactin also showed lower responsiveness to infant cues while males who had the highest levels of testosterone prior to infant birth also show the most responsiveness to infant cues. Additionally causal studies indicate that prolactin helps regulate weight in marmosets and tamarin monkeys. Lowering prolactin is associate with fathers losing a significant amount of weight during the infant period while increasing prolactin prevents weight loss with infant care. We suggest that there are hormonal conditions that faciliate male parental care in the marmoset monkey. This research used WNPRC Assay Services. NIH MIMH funding ended before this reporting period;three publications have resulted.